Suicide Squad 1's relative success was a case more of pre-hype.
Like Batman v Superman there was a lot of hype, people were invested in it and came out in droves to check out. So the opening weeks were decent, but once people actually saw the movie died because they realized it was awful. So the movie wasn't as successful as they expected.
Its negative word of mouth. Its exactly what happened to Ant-Man Quantummania. Lot of hype but once the actual movie came out the hype stopped dead and the profits trickled down quickly.